Thin Film Electrochemical Cell for Lithium Polymer Batteries and Manufacturing Method Therefor

ABSTRACT

An electrochemical cell sub-assembly and a method for manufacturing same. The electrochemical cell sub-assembly includes a current collector sheet having a pair of opposite surfaces and a pair of opposite edges, each surface being coated with a respective layer of electrode material. A layer of polymer electrolyte envelopes both layers of electrode material and one of the pair of edges of the current collector sheet, thereby encapsulating the one edge of the current collector sheet while leaving exposed the other edge of the current collector sheet.

FIELD OF INVENTION

The present invention relates generally to lithium polymer batteries andmore specifically to the design and method of manufacturing of theelectrochemical cells making up a lithium polymer battery.

BACKGROUND OF THE INVENTION

Rechargeable batteries manufactured from laminates of solid polymerelectrolytes and sheet-like anodes and cathodes display many advantagesover conventional liquid electrolyte batteries. These advantages includehaving a lower overall battery weight, a high power density, a highspecific energy and a longer service life, as well as beingenvironmentally friendly since the danger of spilling toxic liquid intothe environment is eliminated.

The components of a solid polymer electrochemical cell include positiveelectrodes, negative electrodes and separators capable of permittingionic conductivity, such as solid polymer electrolytes, sandwichedbetween each anode and cathode. The anodes (or negative electrodes) andcathodes (or positive electrodes) are made of material capable ofreversible insertion of alkali metal ions. The polymer electrolyteseparators electrically isolate the anode from the cathode to preventshort circuits therebetween, which would render the electrochemical celluseless.

The cathodes are typically formed of a mixture of active materialcapable of occluding and releasing lithium, such as transitional metaloxides or phosphates, an electronically conductive filler, usuallycarbon or graphite or combinations thereof, and an ionically conductivepolymer binder. Cathode materials are usually paste-like and require acurrent collector, usually a thin sheet of electrically conductivematerial such as aluminum foil. The anodes are typically made oflight-weight metal foils, such as alkali metals and alloys, typicallylithium metal, lithium oxide, lithium-aluminum alloys and the like. Theanodes may also be composite paste-like material comprising, forexample, carbon-based intercalation compounds in a polymer binder, inwhich case the anode also requires a current collector support,preferably a thin sheet of copper.

Composite cathode thin films are usually obtained by solvent coatingonto a current collector or by melt extrusion. Similarly, the polymerelectrolyte separator layer is typically produced by solvent coating orby melt extrusion.

Solid lithium polymer electrochemical cells are typically manufacturedby successive layering of the positive electrode, the electrolyteseparator and the negative electrode. The positive electrode material isinitially coated or extruded onto a metallic foil (for example aluminum)or onto a metallized plastic film, which serves as a current collector.The polymer electrolyte separator is thereafter preferably coated orextruded directly onto the previously coated cathode material and thenegative electrode is finally laminated onto the electrolyte to form anelectrochemical cell. To increase the energy density of anelectrochemical cell, a bi-face design is preferred wherein positiveelectrode material is laminated, coated or extruded onto both sides ofthe current collector.

Electrochemical cells as previously described are assembled in an offsetpattern: the metallic anode or negative current collector extends fromone side of the electrochemical cell, while the cathode currentcollector extends from the other side of the electrochemical cell. Theelectrolyte separator (or separators in the case of bi-face designs) ispositioned in between the anode and the cathode but does not extend theentire width of the electrochemical cell because a portion of themetallic anode or negative current collector on one side and a portionof the cathode current collector on the other side must remain exposedfor lateral collection of current (i.e. to allow for connection inparallel to other electrochemical cells and to the positive and negativeterminals of the electrochemical generator of which it is a constituentof). The exposed anodes and cathodes may in some circumstances toucheach other when the electrochemical cells are assembled and pressedtogether, resulting in a short circuit which renders the cells useless.Short circuits may also occur through misplacement or misalignment ofthe various layers of the electrochemical cells or through misplacementor misalignment of a stack of electrochemical cells.

To alleviate this potential problem, U.S. Pat. No. 5,360,684 disclosedthe addition of an insulating band of polypropylene or other plasticmaterial between the exposed ends of the anode and the cathode currentcollector, for the sole purpose of eliminating potential short circuit.U.S. patent application Ser. No. 09/876,567 (publication No.US2002/0197535A1) discloses a variant of the same concept, in which aninsulating edge material is coated or extruded at the end of the cathodematerial to prevent a potential short circuit between the exposed endsof the anode and the cathode layer. U.S. Pat. No. 5,670,273 discloses amethod of fabricating electrochemical cells, wherein the successiveanode and cathode layers are separated by a polymeric electrolyte layerhaving a protruding polymer edge that reduces the likelihood ofinadvertent contact between the anode and cathode current collectors.

The above described solutions all fulfill their purpose, however at thecost of either adding steps to the manufacturing process of theelectrochemical cells or having protruding separators that hinder properparallel connections of the current collectors and may cause potentialweight penalties.

Thus, there is a need for an electrochemical cell configuration thatprevents inadvertent short circuits between the anode and cathode, aswell as for a reliable method and apparatus for the production ofelectrochemical cell sub-assemblies for lithium polymer batteries.

STATEMENT OF THE INVENTION

It is therefore an object of the present invention to provide anelectrochemical cell configuration that prevents inadvertent shortcircuits between the anode and cathode.

It is another object of the present invention to provide a method ofmanufacturing sub-assembly components for a thin film electrochemicalcell.

It is a further object of the present invention to provide anelectrochemical generator comprising a plurality of electrochemicalcells configured to prevent inadvertent short circuits between theanodes and cathodes.

As embodied and broadly described, the present invention provides amethod for manufacturing an electrochemical cell sub-assembly for alithium polymer battery, the method including:

-   (a) providing a current collector sheet having a pair of opposite    surfaces and a pair of opposite edges, where each surface is coated    with a respective layer of electrode material;-   (b) extruding a layer of polymer electrolyte over the current    collector sheet such that the layer of polymer electrolyte envelopes    both layers of electrode material and one of the pair of edges of    the current collector sheet, thereby encapsulating the one edge of    the current collector sheet while leaving exposed the other edge of    the current collector sheet.

As embodied and broadly described, the present invention also providesan electrochemical cell including:

-   (a) a positive electrode including:    -   a current collector sheet having a pair of opposite surfaces and        a pair of opposite edges;    -   a layer of positive electrode material disposed on each surface        of the current collector sheet;-   (b) a polymer electrolyte separator encapsulating both layers of    positive electrode material and one of the pair of edges of the    current collector sheet, thereby leaving the other edge of the    current collector sheet exposed; and-   (c) at least one negative electrode disposed over said polymer    electrolyte separator.

As embodied and broadly described, the present invention furtherprovides an electrochemical cell sub-assembly including:

-   (a) a current collector sheet having a pair of opposite surfaces and    a pair of opposite edges, each surface being coated with a    respective layer of electrode material;-   (b) a layer of polymer electrolyte enveloping both layers of    electrode material and one of the pair of edges of the current    collector sheet, thereby encapsulating the one edge of the current    collector sheet while leaving exposed the other edge of the current    collector sheet.

As embodied and broadly described, the present invention also provides asystem for manufacturing an electrochemical cell sub-assembly, thesystem including:

-   (a) a conveyor mechanism transporting a current collector sheet    having a pair of opposite surfaces and a pair of opposite edges,    each surface of the current collector sheet being coated with a    respective layer of electrode material;-   (b) an extrusion die having a pair of distinct discharge nozzles and    a passageway disposed generally in between the distinct discharge    nozzles, the passageway operative to receive the current collector    sheet from the conveyor mechanism, each discharge nozzle operative    to discharge a film of polymer electrolyte onto a respective surface    of the current collector sheet when the current collector sheet    travels through the passageway, thereby encapsulating both Layers of    electrode material and one of the pair of edges of the current    collector sheet, while leaving exposed the other edge of the current    collector sheet.

As embodied and broadly described, the present invention also provides amethod for manufacturing an electrochemical cell sub-assembly for aLithium polymer battery, said method comprising:

-   (a) providing a current collector sheet having a pair of opposite    surfaces and a pair of opposite edges, where each surface is coated    with a respective layer of electrode material;-   (b) laminating a layer of polymer electrolyte over each surface of    the current collector sheet such that the layers of polymer    electrolyte envelope both layers of electrode material and one of    the pair of edges of the current collector sheet, thereby    encapsulating the one edge of the current collector sheet while    leaving exposed the other edge of the current collector sheet.

As embodied and broadly described, the present invention also provides asystem for manufacturing an electrochemical cell sub-assembly for aLithium polymer battery, said system comprising:

-   (a) a conveyor mechanism transporting a current collector sheet    having a pair of opposite surfaces and a pair of opposite edges,    each surface of said current collector sheet being coated with a    respective layer of electrode material;-   (b) a lamination apparatus having a pair of pressure rollers, said    pressure rollers defining a passageway therebetween for receiving    said current collector sheet from said conveyor mechanism, each    pressure roller operative to Laminate a polymer electrolyte layer    onto a respective surface of said current collector sheet when said    current collector sheet travels through said passageway, thereby    encapsulating both said layers of electrode material and one of the    pair of edges of said current collector sheet, while leaving exposed    the other edge of said current collector sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and other advantages will appearby means of the following description and the following drawings inwhich:

FIG. 1 is a schematic cross-sectional view of a electrochemical cellsub-assembly, in accordance with an embodiment of the present invention;

FIG. 2 is a schematic cross-sectional view of an electrochemical cell,in accordance with an embodiment of the present invention;

FIG. 3 is a schematic side elevational view of an extrusion process forencapsulating the electrode layers previously deposited on a currentcollector with a polymer electrolyte, in accordance with an example ofimplementation of the present invention;

FIG. 4 is a schematic top plan view of the extrusion process illustratedin FIG. 3, showing a current collector and electrode assembly travelingthrough the extrusion die;

FIG. 5 is a schematic cross-sectional view of the extrusion die of FIG.3 applying an electrolyte layer on both sides of a current collector andelectrode assembly;

FIG. 6 is a schematic cross-sectional view of an electrochemical cellsub-assembly resulting from the process illustrated in FIG. 3;

FIG. 7 is a schematic cross-sectional view of an extrusion process forencapsulating the electrode layers previously deposited on a currentcollector, in accordance with another example of implementation of thepresent invention;

FIG. 8 is a schematic top cross sectional view of the opposing extrusiondies of FIG. 7 applying an electrolyte layer on a both sides of acurrent collector and electrode assembly;

FIG. 9 is a schematic cross-sectional view of an electrochemical cellsub-assembly resulting from the process illustrated in FIG. 7;

FIG. 10 is a schematic side elevational view of an extrusion process forencapsulating the electrode layers previously deposited on a currentcollector, in accordance with yet another example of implementation ofthe present invention;

FIG. 11 is a schematic side elevational view of an extrusion process forencapsulating the electrode layers previously deposited on a currentcollector, in accordance with another example of implementation of thepresent invention;

FIG. 12 is a schematic side elevational view of an extrusion process forencapsulating the electrode layers previously deposited on a currentcollector, in accordance with another example of implementation of thepresent invention;

FIG. 13 is a schematic cross sectional view of the first extrusion diesof FIGS. 10, 11 and 12 depositing a first layer of polymer electrolyteonto a first side of a current collector and electrode assembly;

FIG. 14 is a schematic cross sectional view of the second extrusion diesof FIGS. 10, 11 and 12 depositing a second layer of polymer electrolyteonto a second side of a current collector and electrode assembly;

FIG. 15 is a schematic cross-sectional view of an electrochemical cellsub-assembly resulting from the process illustrated in each of FIGS. 10,11 and 12;

FIG. 16 is a schematic side elevational view of a lamination process forencapsulating the electrode layers previously deposited on a currentcollector, in accordance with yet another example of implementation ofthe present invention;

FIG. 17 is a schematic cross-sectional view taken at line 17-17 of FIG.16;

FIG. 18 is a schematic cross-sectional view taken at line 18-18 of FIG.16;

FIG. 19 is a schematic cross-sectional view of a dual electrochemicalcell sub-assembly, in accordance with a variant embodiment of thepresent invention;

FIG. 20 is a schematic cross-sectional view of a pre-assembly of a largecurrent collector previously coated with layers of electrode material,in accordance with another variant embodiment of the present invention;

FIG. 21 is a schematic cross-sectional view of the pre-assemblyillustrated in FIG. 20 after being cut; and

FIG. 22 is a schematic cross-sectional view of the pre-assembliesillustrated in FIG. 21, encapsulated with polymer electrolyte envelopes.

DETAILED DESCRIPTION

With reference to FIG. 1, there is shown a cross-section of anelectrochemical cell sub-assembly 10, in accordance with an embodimentof the present invention. The electrochemical cell sub-assembly 10includes a central current collector element 12, a layer of electrodematerial 14 coated on each surface of the central current collectorelement 12 and a polymer electrolyte 16. The polymer electrolyte 16completely envelopes the layers of electrode material 14 coated on thesurfaces of the central current collector element 12, as well as oneedge 13 of the current collector element 12. In this example, the layerof electrode material 14 consists of a cathode or positive electrodematerial. The polymer electrolyte envelope 16 is ionically conductivebut electrically non-conductive, as is well known in the art, in orderto allow ionic exchanges between the positive and negative electrodesbut inhibit the formation of electrical current pathway between thepositive and negative electrodes of the electrochemical cell. As shownin FIG. 1, the electrode layers 14 and one edge 13 of the centralcurrent collector 12 are completely enclosed within the polymerelectrolyte envelope 16 and therefore are completely isolatedelectrically. Only edge 15 of the central current collector 12 remainsexposed for the purpose of electrical connection to otherelectrochemical cells or to the electrical post of the generator havingat least one electrochemical cell.

FIG. 2 illustrates a complete electrochemical cell 20, in accordancewith an embodiment of the present invention. The electrochemical cell 20is formed of the sub-assembly 10, which includes the central currentcollector element 12, the layers of electrode material 14 coated on eachsurface of the central current collector element 12 and the polymerelectrolyte envelope 16, which completely envelopes the layers ofelectrode material 14. A negative electrode 18 is disposed on each sideof the polymer electrolyte envelope 16 facing the layers of positiveelectrode material 14, thereby sandwiching the polymer electrolyteenvelope 16 and completing the electrochemical cell 20. As illustrated,the layers of positive electrode material 14 and edge 13 of the centralcurrent collector element 12 are completely isolated electrically fromthe negative electrodes 18, thereby reducing the risks of short circuitsbetween the negative electrodes 18 and either the positive electrodematerial 14 or the edge 13 of the central current collector element 12.In this particular configuration, the positive and negative electricalcontact points are offset. More specifically, the current collectorelement 12 of the positive electrode extends to one side of theelectrochemical cell 20, while the negative electrodes 18 extend to theother side of the electrochemical cell 20, such that the electricalcontact points are on opposite sides of the electrochemical cell 20. Asis well known in the art, a plurality of electrochemical cells may bestacked together, their positive electrodes connected together inparallel and their negative electrodes also connected in parallel, toincrease their overall capacity (Amp/hr).

The electrochemical cells described herein are typically formed ofextremely thin constituents. For example:

-   -   the thickness of the central current collector element 12 may        range from 12 μm to 50 μm;    -   the thickness of one layer of positive electrode material 14 may        range from 15 μm to 100 μm;    -   the thickness of one side of the polymer electrolyte envelope 16        may range from 15 μm to 50 μm; and    -   the thickness of the negative electrode 18 may range from 20 μm        to 80 μm.

The above thickness ranges are given only as an example, in order toillustrate the difficulty of producing such an assembly. Other thicknessranges for each of the central current collector element 12, thepositive electrode material 14, the polymer electrolyte envelope 16 andthe negative electrode 18 are also possible and included within thescope of the present invention.

FIGS. 3 and 4 illustrate an example implementation of an apparatus andmethod for overlaying a central current collector element having layersof electrode material on both its surfaces with a polymer electrolyteenvelope, in order to form the electrochemical cell sub-assembly 10illustrated in FIG. 1, in accordance with an embodiment of the presentinvention. A pre-assembly 22, including a current collector element 12that was previously coated on both its surfaces with Layers of electrodematerial 14, is delivered via a conveyor mechanism, in this example aseries of cylindrical rollers 34, to a dual extrusion die 30, where thinlayers of polymer electrolyte 24 are overlaid onto each side of thepre-assembly 22. A single screw or twin screw extruder 31 feeds polymerelectrolyte material to the dual extrusion die 30.

As illustrated in FIGS. 3 and 4, the pre-assembly 22 travels throughdual extrusion die 30, where a thin layer of polymer electrolyte 24 isapplied simultaneously to both sides of the pre-assembly 22. As seenmore clearly in FIG. 4, the layers of polymer electrolyte 24 are widerthan the layers of electrode material 14, such that the two layers ofpolymer electrolyte 24 completely encapsulate the layers of electrodematerial 14 and also circumvent one edge 13 of the current collector 12.The pre-assembly 22 with its polymer electrolyte envelope 16 is thenredirected by a series of cylindrical rollers 32A and 32B, which arepreferably maintained at a cool temperature in order to accelerate thesolidification of the polymer electrolyte envelope 16 and to preventunwanted adhesion of the polymer to the rollers. The completeelectrochemical cell sub-assembly 10 (FIG. 1) is then routed towardsother stations for further processing or storage.

FIG. 5 illustrates schematically a cross-sectional view of the dualextrusion die 30 of FIGS. 3 and 4, when the pre-assembly 22 travelsdirectly therethrough.

Extrusion die 30 includes two discharge nozzles 35 and 37, illustratedin dotted lines, which determine the path that the polymer electrolytefollows inside the extrusion die 30 before being discharged as a thinsheet onto both sides of the pre-assembly 22. The polymer electrolytematerial is fed to the extrusion die 30 under pressure from the extruder31 (FIGS. 3 and 4) through a cylindrical channel 39. Upon entering theextrusion die 30, the polymer electrolyte material is divided by a flowdivider 44 into two separate internal channels 41 and 43, leading to thedischarge nozzles 35 and 37, respectively. When entering the dischargenozzles 35 and 37, the polymer electrolyte material is shaped into awide but thin film. This film is discharged over an area that covers thelayers of electrode material 14, the entire edge 13 of the currentcollector element 12 and a portion of the other end 15 of the currentcollector element 12. Accordingly, the two layers of electrode material14 are enveloped and electrically isolated.

FIG. 6 illustrates schematically a cross sectional view of theelectrochemical cell sub-assembly 10 exiting the dual extrusion die 30,where it can be seen that the two layers of polymer electrolyte 24 mergetogether at a meeting point 45 beyond the end of the edge 13 of currentcollector 12, thereby forming the polymer electrolyte envelope 16.

FIG. 7 illustrates another example of implementation of an apparatus andmethod for overlaying a central current collector element having layersof electrode material on both its surfaces with a polymer electrolyteenvelope, in order to form the electrochemical cell sub-assembly 10illustrated in FIG. 1. A pre-assembly 22 formed of a current collectorelement 12 that was previously coated on both its surfaces with layersof electrode material 14 is delivered via a series of cylindricalrollers 48 (only one shown) to a pair of extrusion dies 50 and 60, wherethin layers of polymer electrolyte 52 and 62 are overlaid simultaneouslyonto respective sides of the pre-assembly 22. Since both layers 52 and62 of polymer electrolyte are wider than the layers of electrodematerial 14, they completely encapsulate the layers of electrodematerial 14. The pre-assembly 22 with its layers 52 and 62 of polymerelectrolyte is next guided by cylindrical roller 55, which is preferablymaintained at a cool temperature in order to accelerate thesolidification of the polymer electrolyte layers and prevent anyunwanted adhesion thereof. The complete electrochemical cellsub-assembly 10 is routed towards other stations for further processingor storage.

FIG. 8 illustrates schematically a top cross sectional view of the pairof opposing extrusion dies 50 and 60 of FIG. 7, when the pre-assembly 22including its layers of electrode material 14 travels directly in frontof the discharge ends of extrusion dies 50 and 60. The internal channels54 and 64 of extrusion dies 50 and 60, respectively, are illustrated indotted lines and determine the path that the polymer electrolyte followsinside each extrusion die 50 and 60 before being discharged as thinsheets onto the surfaces of the pre-assembly 22. The polymer electrolytesheets 52 and 62 are spread over an area covering the layers ofelectrode material 14 and extending marginally beyond edge 13 of thecurrent collector element 12, in order to envelop and electricallyisolate the end of edge 13. The polymer electrolyte sheets 52 and 62also extend over a portion of the other end 15 of the current collectorelement 12, thereby enveloping and electrically isolating the two Layersof electrode material 14.

FIG. 9 illustrates the electrochemical cell sub-assembly 10 resultingfrom the apparatus and method of extrusion shown in and described withregard to FIGS. 7 and 8. As previously mentioned, the polymerelectrolyte sheets 52 and 62 are discharged over an area that extendsmarginally beyond edge 13 of the current collector element 12, such thatthe polymer electrolyte sheets 52 and 62 merge beyond the edge 13thereby enclosing the edge 13 and forming the polymer electrolyteenvelope 16.

Although FIG. 7 illustrates extrusion dies 50 and 60 directly opposed toeach other, they may be offset relative to one another.

FIG. 10 illustrates a variant example of implementation of the apparatusand method for overlaying a central current collector element havinglayers of electrode material on both its surfaces with a polymerelectrolyte envelope, in order to form the electrochemical cellsub-assembly 10 illustrated in FIG. 1. In this example, the extrusiondies 70 and 80 are offset relative to each other. The pre-assembly sheet22 is preferably supported by cylindrical rollers 74 and 84 when thelayers of polymer electrolyte 72 and 82 are applied onto the travelingpre-assembly sheet 22. The polymer electrolyte Layers or sheets 72 and82 are discharged over an area that extends marginally beyond the edge13 of the current collector element 12. Accordingly, the polymerelectrolyte sheets 72 and 82 completely overlay the layers of electrodematerial 14 and merge beyond the edge 13, thereby enclosing the edge 13and forming the polymer electrolyte envelope 16, as illustrated withmore detail in FIG. 15.

FIG. 11 illustrates another variant example of implementation of theapparatus and method for overlaying a central current collector elementhaving layers of electrode material on both its surfaces with a polymerelectrolyte envelope, in order to form the electrochemical cellsub-assembly 10 illustrated in FIG. 1. In this example, the extrusiondies 90 and 100 are disposed in a marginally different configurationthan that illustrated in FIG. 10, although the extrusion dies 90 and 100are still offset relative to each other. The pre-assembly sheet 22 issupported by cylindrical rollers 94 and 104 when the layers of polymerelectrolyte 92 and 102 are applied onto the traveling pre-assembly sheet22. As previously described with reference to FIG. 8, the polymerelectrolyte layers or sheets 92 and 102 are discharged over an area thatextends marginally beyond the edge 13 of the current collector element12. Accordingly, the polymer electrolyte sheets 92 and 102 completelyoverlay the layers of electrode material 14 and merge beyond the edge13, thereby enclosing the edge 13 and forming the polymer electrolyteenvelope 16, as illustrated with more detail in FIG. 15.

FIG. 12 illustrates yet another variant example of implementation of theapparatus and method for overlaying a central current collector elementhaving layers of electrode material on both its surfaces with a polymerelectrolyte envelope, in order to form the electrochemical cellsub-assembly 10 illustrated in FIG. 1. In this example, the pre-assembly22 is delivered via a series of cylindrical rollers 112 (only one shown)to a first extrusion die 110, where a thin layer of polymer electrolyte24 is overlaid onto a first side of the pre-assembly 22.

As previously described, the layer of polymer electrolyte 24 is widerthan the layer of electrode material, such that it completelyencapsulates the layer of electrode material. The pre-assembly 22 withthe added layer of polymer electrolyte 24 on one of its surfaces is thenredirected by a cylindrical roller 114, which is preferably maintainedat a cool temperature in order to accelerate the solidification of thepolymer electrolyte layer 24. The pre-assembly 22 with the added layerof polymer electrolyte 24 is then delivered via another series ofcylindrical rollers 116 (only one shown) to a second extrusion die 120,where another thin layer of polymer electrolyte 24 is overlaid onto thesecond side of the pre-assembly 22. Again, the layer of polymerelectrolyte 24 being applied on the second side of the pre-assembly 22is wider than the layer of electrode material, such that it completelyencapsulates the layer of electrode material. The pre-assembly 22 withboth layers of polymer electrolyte 24 forming an envelope 16 issupported by cylindrical roller 118, which is also preferably maintainedat a cool temperature in order to accelerate the solidification of thesecond polymer electrolyte layer 24 and to prevent unwanted adhesion ofthe first layer of polymer electrolyte 24. The complete electrochemicalcell sub-assembly 10 is routed towards other stations via another seriesof cylindrical rollers 122 (only one shown) for further processing orstorage.

FIG. 13 illustrates schematically a cross sectional view of each of thefirst extrusion dies 70, 90 and 110 of FIGS. 10, 11 and 12,respectively, when the pre-assembly 22 travels directly in front of thedischarge end of the extrusion die. The internal channel 125 of theextrusion die 70, 90, 110 is illustrated in dotted lines and determinesthe path that the polymer electrolyte follows inside the extrusion die70, 90, 110 before being discharged as a thin film onto a first side ofthe pre-assembly 22. The polymer electrolyte sheet 24 is spread over anarea that covers the first layer of electrode material 14, the entireedge 13 of the current collector element 12 and a portion of the otheredge 15 of the current collector element 12, thereby enveloping andelectrically isolating the first layer of electrode material 14.

FIG. 14 illustrates schematically a cross sectional view of each of thesecond extrusion dies 80, 100 and 120 of FIGS. 10, 11 and 12,respectively, when the pre-assembly 22 including the first added polymerelectrolyte layer 24 travels directly in front of the discharge end ofthe extrusion die with the second side or surface of the pre-assembly 22facing the extrusion die. The internal channel 127 of the extrusion die80, 100, 120 is illustrated in dotted lines and determines the path thatthe polymer electrolyte follows inside the extrusion die 80, 100, 120before being discharged as a thin film onto the second side or surfaceof the pre-assembly 22. The polymer electrolyte sheet 26 is spread overan area that covers the second layer of electrode material 14 andextends marginally beyond edge 13 of the current collector element 12,in order to envelop and electrically isolate the end of edge 13. Thepolymer electrolyte sheet 26 also extends over a portion of the otherend 15 of the current collector element 12, thereby enveloping andelectrically isolating the second layer of electrode material 14.

FIG. 15 illustrates the electrochemical cell sub-assembly 10 resultingfrom the apparatuses and methods of extrusion shown in and describedwith regard to FIGS. 10 to 14. As previously described, the polymerelectrolyte sheet 26 is discharged over an area that extends marginallybeyond edge 13 of the current collector element 12. As such, it foldsover the edge 13 by capillarity to enclose the edge 13 and adhere topreviously applied polymer electrolyte layer 24, for forming the polymerelectrolyte envelope 16.

FIG. 16 illustrates another variant example of implementation of theapparatus and method for overlaying a central current collector elementhaving layers of electrode material on both its surfaces with a polymerelectrolyte envelope, in order to form the electrochemical cellsub-assembly 10 illustrated in FIG. 1. In this example, the polymerelectrolyte envelope 16 is formed by laminating polymer electrolytefilms 24 onto the electrode layers 14 of each surface of the centralcurrent collector 12. As illustrated in FIG. 16, a pre-assembly 22,including a current collector element 12 that was previously coated onboth its surfaces with layers of electrode material 14, is delivered viaany conveyor system to a first pair of rollers 200, where thin films ofpolymer electrolyte 24 are overlaid onto each side of the pre-assembly22. Alternatively, the polymer electrolyte films 24 may be overlaid ontothe respective sides of the pre-assembly 22 at different locations andin successive steps, as opposed to the simultaneous applicationillustrated in FIG. 16.

In a specific example, each thin film of polymer electrolyte 24 has beenpreviously laid onto a plastic support film 202, covered by anotherprotective plastic film 204 and wound into a roll 201, 203 for storage.As illustrated in FIG. 16, the protective plastic films 204A and 204Bare peeled off of the thin films of polymer electrolyte 24, routed awayfrom the rollers 200 and wound onto recuperation rolls 205 and 207, inorder to expose the polymer electrolyte films 24 to the layers ofelectrode material 14 prior to lamination. The polymer electrolyte films24 are then brought into contact with the layers of electrode material14 such that they are offset to one side of the pre-assembly 22, as seenin FIG. 17. More specifically, both polymer electrolyte films 24 extendover one edge 206 of the pre-assembly 22, and thus over one edge of thecentral current collector 12 of the pre-assembly 22, such that theextensions 210 of the polymer electrolyte layers 24 may be brought intocontact with each other when the entire assembly is pressed together.The ends 208 of the polymer electrolyte films 24 also extend past theends of the layers of electrode material 14, in order to encapsulatethem when the entire assembly is pressed together.

The laminate 212 formed of a central current collector 12, two layers ofelectrode material 14, as well as a layer of polymer electrolyte 24 anda plastic support film 202 on each side thereof, next enters a heatingzone 215. In this heating zone 215, the two layers of polymerelectrolyte 24 are heated to a temperature sufficient to promoteadhesion of the polymer electrolyte layers 24 onto the electrode layers14, as well as adhesion of the extensions 210 of the polymer electrolytelayers 24 to each other. The heat may be generated by any means known tothose skilled in the art.

The heated laminate 212 then passes through a pair of lamination rollers216, at least one of which is covered with a layer of rubber or otherflexible material in order to conform to the profile of the laminate 212and exert a pressure P onto the entire surface of the respective polymerelectrolyte film 24. Accordingly, the extensions 210 of the polymerelectrolyte layers 24 adhere to each other and envelop the edge of thecentral current collector 12, while the ends 208 of the polymerelectrolyte layers 24 enclose the ends of the electrode material Layers14. As a result, the polymer electrolyte layers 24 encapsulate theentire electrode layers 14 and one edge of the central current collector12, as illustrated in FIG. 18.

Thereafter, the laminate 212 is routed through a series of coolingrollers 217 and 219. The cooling rollers 217 and 219 are maintained at atemperature below room temperature (10° to 15° C.). The laminate 212 ismaintained in contact with the cooling rollers 217, 219 as it travelsover an arc of the circumference of each roller 217, 219, this beingsufficiently long for the laminate 212 to dissipate its residual heatvia the cooling rollers 217, 219.

The laminate 212 is then routed to a peeling station 220, where theplastic support films 202 are removed from the laminate 212 and woundonto recuperation rolls 221 and 223. To prevent any damage to thepolymer electrolyte films 24 encapsulating the electrode Layers 14 whilethe plastic support films 202 are being removed, a suitable solvent isintroduced at each peeling point 222 and 224. This solvent reduces theadhesion forces between the polymer electrolyte layers 24 and theplastic support films 202, thus preventing any ripping of portions orsegments of the polymer electrolyte films 24. As illustrated in FIG. 16,the peeling angles are less than 90°. In this manner, each pair ofplastic support film 202 and polymer electrolyte film 24, onceseparated, forms a small pool where the solvent can remain and act onthe interface between the plastic support film 202 and polymerelectrolyte film 24.

Note that a small quantity of solvent may remain on the surface of eachpolymer electrolyte film 24. As such, the laminate 10 is next passedthrough a drying station 226, where the excess or remaining solvent isevaporated.

In order to store the encapsulated laminate 10, a new protective film230 having a weak adherence to the polymer electrolyte is appliedthereto in order to prevent adhesion of adjacent layers of polymerelectrolyte 24 when the laminate 10 is wound onto a roll 229, as well asto ease peeling when the laminate 10 is brought for final assembly withthe anode portions of the electrochemical cell. Of course, the laminate10 may alternatively be brought directly to a further processing stationfor assembly into a complete electrochemical cell.

FIG. 19 illustrates a variant embodiment of the present invention, inwhich a large current collector element 150 is coated on each of itssurfaces with two separate layers of electrode material. Morespecifically, layers 152 and 153 coat the first surface of the currentcollector element 150, while layers 154 and 155 coat the second surfaceof the current collector element 150. The layers of electrode material152, 153 and 154, 155 are then encapsulated by two distinct polymerelectrolyte envelopes 158 and 159, which also circumvent the edges 160and 161, respectively, of the current collector element 150 to form adual sub-assembly 175. As shown in FIG. 19, the electrode layers 152,153 and 154, 155, as well as the two edges 160 and 161 of the currentcollector element 150, are completely enclosed and thus electricallyisolated within the two polymer electrolyte envelopes 158 and 159. Onlythe intermediate portion 165 of the current collector element 150remains exposed. In a subsequent step in the manufacturing process, thecurrent collector element 150 is slit along the axis A-A at the midpointof the intermediate portion 165, in order to form two separateelectrochemical cell sub-assemblies 10 as illustrated in FIG. 1. Theexposed edges of the previously slit current collector element 150allows for electrical connection to other electrochemical cells or tothe electrical post of the generator formed of a series of stackedelectrochemical cells.

Any of the apparatuses previously described and shown in FIGS. 3, 7, 10,11, 12 and 16 are suitable to produce the dual sub-assembly 175 shown inFIG. 19. However, the apparatuses which extrude polymer electrolytelayers will include extrusion dies having two separate internalchannels, one for each polymer electrolyte layer, such that the layersof polymer electrolyte can be extruded to form the polymer electrolyteenvelopes 158 and 159 shown in FIG. 19. Furthermore, the apparatuseswhich laminate the polymer electrolyte layers onto the pre-assembly 22will be fed with two pairs of parallel polymer electrolyte films, inorder to cover both electrode layers and both edges of the centralcurrent collector 150 prior to slitting. The slitting of thesub-assembly 175 may be done by any conventional method.

In another variant embodiment of the present invention, FIG. 20illustrates a large current collector element 250 coated with a largelayer of electrode material 252 on each of its surfaces, leaving bothedges 253 and 254 of the large current collector element 250 exposed. Ina subsequent step of the manufacturing process, the pre-assembly formedof current collector element 250 and electrode layers 252 is slit or cutalong the axis A-A at the midpoint, in order to form the two separatepre-assemblies 255 shown in FIG. 21. The ends of the current collectorelement 250 and of the electrode layers 252 on the cut sides 256 of thepre-assemblies 255 are therefore even, while the edges 253 and 254remain exposed.

In a final step of the manufacturing process illustrated in FIG. 22,polymer electrolyte layers 258 and 259 are coated onto pre-assemblies255 by any method previously described, such that the polymerelectrolyte layers 258 and 259 encapsulate the entire electrode layers252, as well as the ends 256, with a polymer electrolyte envelope 260.Thus, the ends 256 are electrically insulated to prevent any potentialshort circuit, while the edges 253 and 254 of the current collectorelement 250 remain exposed to allow for electrical connection to otherelectrochemical cells or to the electrical post of a generator formed ofa series of stacked electrochemical cells.

Although the present invention has been described in relation toparticular variations thereof, other variation and modifications arecontemplated and are within the scope of the present invention.Therefore the present invention is not to be limited by the abovedescription but is defined by the appended claims.

1. An electrochemical cell comprising: a. a positive electrodeincluding: i. a current collector sheet having a pair of oppositesurfaces and a pair of opposite edges; and ii. a layer of positiveelectrode material disposed on each surface of the current collectorsheet, one of the opposite edges of the current collector sheetextending to one side of the two layers of positive electrode material;b. an ionically conductive polymer electrolyte separator encapsulatingboth layers of positive electrode material and the other edge of thecurrent collector sheet, thereby leaving exposed the one edge of thecurrent collector sheet extending to one side of the two layers ofpositive electrode material; and c. at least one negative electrodedisposed over said polymer electrolyte separator and having one edgeextending in the opposite direction of the exposed edge of the currentcollector sheet.
 2. An electrochemical cell as defined in claim 1,wherein said at least one negative electrode extends outwardly from saidencapsulated edge of said current collector sheet, such that saidnegative electrode is spaced apart from said exposed edge of saidcurrent collector sheet.
 3. An electrochemical cell as defined in claim1, comprising a pair of negative electrodes, each negative electrodebeing disposed adjacent a respective surface of said current collectorsheet, over said polymer electrolyte separator, thereby forming abi-face electrochemical cell.
 4. An electrochemical cell as defined inclaim 3, wherein each of said negative electrodes extends outwardly fromsaid encapsulated edge of said current collector sheet, such that eachof said negative electrodes is spaced apart from said exposed edge ofsaid current collector sheet.
 5. An electrochemical cell sub-assemblycomprising: a. a current collector sheet having a pair of oppositesurfaces and a pair of opposite edges, each surface being coated with arespective layer of electrode material; and b. a layer of polymerelectrolyte enveloping both layers of electrode material and one of thepair of opposite edges of said current collector sheet, therebyencapsulating the one edge of said current collector sheet while leavingexposed the other edge of said current collector sheet.